Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing, bridging makes no assumptions about where in a network a particular address is located. Instead, bridging depends on flooding and examining source addresses in received packet headers to locate unknown devices. Once a device has been located, the device's location is recorded in a table where a media access control (MAC) address is stored so as to preclude the need for further broadcasting. Bridging generally refers to transparent bridging or a learning bridge operation which predominates in the Ethernet.
A network bridge connects multiple network segments at the data link layer (Layer 2) of the Open Systems Interconnection (OSI) model. In Ethernet networks, the term “bridge” refers to a device that behaves according to the IEEE 802.1d standard. The terms “switch” or “Layer 2 switch” are often used interchangeably with the term “bridge.” Bridges are similar to repeaters or network hubs, which are devices that connect network segments at the physical layer (Layer 1) of the OSI model. However, with bridges, traffic from one network is managed rather than simply rebroadcast to adjacent network segments. A bridge can analyze incoming packets to determine if the bridge is able to send the given packet to another segment of the network.
However, network bridges are, by nature, not scalable due to the network bridges' extensive use of flooding (e.g., a scalability issue). Furthermore, network bridges always force a single link connectivity that is prone to topology disturbances and is unable to use multiple shortest paths (e.g., a resiliency issue). Network bridges are also less able to support bi-sectional traffic, which creates several half-utilized network segments (e.g., an efficiency issue). One attempt to solve such issues with network bridges involves using transparent interconnections of lots of links (referred to as TRILL). Another attempt to solve the issues with network bridges is referred to as shortest path bridging (SPB) pursuant to the IEEE 802.1aq standard. However, both TRILL and SPB require implementation of new hardware in network devices, such as network bridges.